🤖 Robot Arm with Servo Claw: step-by-step build

Swing, lift and grab! Three motors and a remote turn you into a factory robot operator.

In car factories, giant robot arms lift, turn and grab all day long. Ours has three motors. The M motor swings the whole robot round on the turntable, the mighty XL motor lifts the arm through a worm gear, and the Servo motor opens and closes the claw. A servo is special: it does not spin round and round, it turns to a position and holds it — perfect for gripping. Use the remote for the arm and the claw, and the switch for turning. Can you move a tower of gears from one side to the other?

• Level 4 of 5 (tricky)
• About 60 minutes
• 30 steps, 91 parts
• Powered by: Multi-motor
• Series: Mechanical Wonders

What you will learn

• Remote Control: Invisible light carries your commands to the model.
• Servo Motor: A motor that turns to an angle and holds it.
• Worm Gear: The Lock: A worm gear turns a gear super slowly — and never slips back.
• Turntables: A turntable lets a whole model spin round.
• Mounting a Motor: A motor must be pinned tight, or it spins itself instead of your wheels.
• Plugging In: Power Functions: Battery box → (switch or receiver) → motor. Plugs stack like bricks.
• Triangles Are Strong: A triangle cannot be squished — a square can.
• Switching Direction: Flip which way electricity flows and the motor spins backwards.

Build these first

• 🦾 XL Power Crane: The strongest motor plus a worm gear: 24 times slower and super strong. (level 4 of 5, about 35 minutes, 27 steps)
• 🏆 RC Racer: A real remote-control car: motor drive, differential, servo steering and headlights. (level 5 of 5, about 75 minutes, 38 steps)

Parts you need

• 1 × Open frame 5×11
• 1 × Turntable
• 15 × Blue long pin
• 10 × Split pin block
• 11 × Red axle-pin
• 1 × L-beam 2×4
• 1 × L-beam 3×5
• 8 × Bush
• 2 × Worm gear
• 1 × Axle 12
• 10 × Black pin (grippy)
• 1 × M motor
• 3 × Beam 7
• 1 × Axle 3
• 1 × Double cross block
• 1 × Open frame 5×7
• 2 × Beam 5
• 1 × Beam 3
• 1 × XL motor
• 2 × Beam 9
• 3 × Half bush
• 1 × Axle 6
• 2 × Beam 11
• 1 × Medium gear (24 teeth)
• 1 × Axle 9
• 1 × Servo motor
• 1 × Axle 10
• 2 × Thin beam 4
• 1 × Axle 7
• 1 × IR receiver
• 1 × AAA battery box
• 1 × Direction switch
• 1 × Speed remote

Steps

1. Lay the white 5×11 frame flat and put the turntable in the middle.
2. Back bearing: push blue long pins up into the 1st and 3rd holes of the frame's back end and slide two split pin blocks down onto them, one on top of the other.
3. Push a red axle pin into each block, pointing in, and press the black 2×4 L-beam onto both, its long leg lying along the end. Its far hole will hold the slewing axle.
4. Motor plate: the same at the front end — two blue long pins in the 1st and 3rd holes and two split pin blocks.
5. Push a red axle pin into each block, pointing out, and press the grey 3×5 L-beam onto both, its long leg lying along the end.
6. Hold a bush, the worm and another bush in a row, the worm touching the turntable's teeth, and push a 12-long axle from the front through the motor plate, the bushes, the worm and the back bearing. The bushes keep the worm from sliding.
7. Push black pins into the plate's holes on both sides of the axle, pointing out, and press the M motor onto the pins and the axle end.
8. Lay a 7-hole beam flat across the turntable and push a 3-long axle down through its middle hole into the turntable. Push a red axle-pin into the beam two holes along, and slide a double cross block down onto the axle and the axle-pin.
9. Push black pins up into the beam's end holes and press the 5×7 frame flat onto them, around the block: the upper deck.
10. Left post: push blue long pins up into the 5th and 7th holes of the deck's left side and slide two split pin blocks onto them, one on top of the other.
11. Right post: the same on the deck's right side.
12. Push a red axle pin into each of the four blocks, pointing out.
13. Stand a 5-hole post on each pair of red pins, just outside the deck.
14. Worm bearing: push blue long pins up into the 2nd and 4th holes of the deck's front end and slide two split pin blocks onto them, one on top of the other.
15. Push a red axle pin into each block, pointing forwards, and press a 3-hole beam onto them, standing up.
16. Shoulder motor: lay the XL motor on its side, output forwards, and push blue long pins into its two left side lugs. Press a 9-hole rail onto them (holes 1 and 6).
17. Do the same on the right: two blue long pins in the right lugs and the second 9-hole rail.
18. Lower the motor and rails onto the deck from above, rails outside the posts. Push a black pin through the 8th hole of each rail into the middle hole of the post.
19. Hold a half bush, the worm gear and another half bush in a row between the posts and push a 6-long axle from the front through the worm bearing, the half bushes and the worm into the XL motor.
20. Put a half bush on the front end of the worm axle so it cannot slide out.
21. Arm: hold an 11-hole beam, the 24-tooth gear and a second 11-hole beam side by side, and push a blue long pin through hole 2 of both beams and the gear's small hole.
22. Push a 9-long axle through the arm tip with a bush on each side.
23. Add two more bushes, one on each side.
24. Hang a 7-hole beam on each end of the tip axle. The claw hangs from them and always points down.
25. Push black pins into holes 2 and 3 of the right hanger, pointing inwards, and press the Servo motor's front pin holes onto them, output at the bottom.
26. Push a 10-long axle through the bottom holes of both hangers and right through the servo. Put a thin 4-hole jaw on each end.
27. Lower the arm between the posts, gear on top of the worm. Hold a bush between each post and the arm and push the 7-long pivot axle through post, bush, arm, gear, arm, bush, post.
28. Push black pins into holes 3 and 5 of the left rail, pointing outwards, and press the IR receiver's back pin holes onto them. XL motor → red side, Servo → blue side.
29. Click the AAA battery box up under the receiver, and the switch onto the free half of the box. Plug the M motor into the switch and stack the receiver plug on the box.
30. Take the speed remote: red dial lifts, blue dial grabs.

Play time

Stack three gears into a tower on one side. Swing, lower, grab, lift, swing and drop — can you rebuild the tower on the other side? Time yourself, then challenge a friend!

Real-world inspiration

Industrial robot arms and claw machines — https://en.wikipedia.org/wiki/Industrial_robot